1. Investigation of systemic arthritis in populations To investigate the role of genetic variation on sJIA susceptibility at the population level, we partnered with colleagues from around the world to establish the International Childhood Arthritis Genetics Consortium (INCHARGE). Working with INCHARGE, we assembled a collection of DNA specimens from over 1000 children with sJIA from North America, South America and Europe. Using this collection, we generated dataset of over 6.7 million common genetic markers or single nucleotide polymorphisms (SNPs) across the entire genome. When combined with genome-wide SNP data from a collection of 8010 geographically matched control subjects, this case-control collection became the basis for the first genomic investigations of sJIA. In the first of these studies, we established that the major histocompatibility complex (MHC) locus on chromosome 6 is the strongest sJIA susceptibility locus. Intensive interrogation of the MHC locus revealed a group of SNPs in the class II human leukocyte antigen (HLA) region that were associated with an increased risk of developing sJIA with an odds ratio of 2.6. The risk SNPs are in strong linkage disequilibrium with a specific class II HLA protein allele, HLA-DRB1*11, and reside on a 250kb sJIA-associated haplotype that includes most of the class II HLA region. The class II HLA proteins encoded by this locus are essential elements of the adaptive immune system that initiate antigen-specific responses by presenting peptide antigens for recognition by CD4-positive T lymphocytes. Given the inflammatory character of sJIA, the body of literature demonstrating innate immune activation/dysfunction in sJIA, and a presumed lack of autoimmunity, this observation was surprising. Mechanistic investigations of this haplotype and how it predisposes to sJIA are ongoing. We expect these studies to reveal important interconnections between adaptive and innate immune dysfunction. To move beyond the MHC locus and examine the rest of the genome, we performed the first genome-wide association study of sJIA. Genome-wide association meta-analysis uncovered 21 previously unreported genetic regions that contribute to sJIA susceptibility. The strongest among these is an intergenic region of chromosome 1, where SNPs were associated with an increased risk of developing sJIA with an odds ratio of 2.4. We observed a conspicuous lack of intersection between the sJIA risk loci and either the set of known JIA susceptibility loci or the set of genes commonly implicated in autoimmune diseases. Moreover, we performed formal genetic comparisons of sJIA with other forms of JIA that clearly demonstrated that sJIA is genetically dissimilar from the other forms of JIA. Based on our discovery of its distinct genetic architecture, combined with its unique inflammatory phenotype, we continue to advocate for the removal of systemic arthritis from future classification schemes of childhood arthritis. In the current reporting period, we again leveraged the INCHARGE GWAS dataset, this time investigating 11 sJIA candidate susceptibility loci that were reported prior to the GWAS era. These loci were identified by small case-control studies and most of the associations were not replicated by subsequent studies. Given that candidate gene studies are susceptible to the potentially detrimental effects of sampling bias and population stratification, we revisited these loci in our large, genetically-matched study population. Among the 11 candidate loci, only the interleukin-1 receptor antagonist (IL1RN) locus demonstrated evidence of association with sJIA. Specifically, sJIA is associated with a cluster of SNPs in the IL1RN promoter that are known to strongly correlate with IL1RN gene expression and serum levels of the interleukin-1 receptor antagonist protein (IL1Ra). Using in silico analyses of published gene expression studies of healthy subjects, we observed that sJIA associated variants were among the strongest predictors of IL1RN expression, with low expression correlating with increased risk of sJIA. Because recombinant IL1Ra (anakinra) is an effective treatment for some patients with sJIA, we hypothesized that these genetic markers may also predict response to anakinra treatment in sJIA. Indeed, in a group of 38 children from the U.S. INCHARGE collection who received anakinra treatment, homozygosity for the high expression IL1RN genotypes in sJIA patients was highly predictive of non-response to anakinra treatment (p = 7.7 times 10 to the negative 4; odds ratio 28.7, 95% confidence interval 3.2 to 256; sensitivity 0.92; specificity 0.71). Based on this finding, these SNPs may be clinically useful as biomarkers to guide the personalized treatment of systemic arthritis. This work was published in Arthritis & Rheumatology. 2. Investigation of systemic arthritis in individuals To investigate whether high-impact genetic variation influences sJIA susceptibility on an individual level, we apply sequencing-based approaches to identify rare genetic variation in subjects with sJIA. We began by leveraging a subset of the INCHARGE collection to perform a targeted deep resequencing study to evaluate whether rare variants of sJIA candidate genes influence disease risk. The candidate genes are divided into 3 groups: genes that showed at least a modest association with sJIA in our GWAS; genes known to cause monogenic autoinflammatory syndromes, which are phenotypically similar to sJIA; and genes known to cause familial forms of hemophagocytic lymphohistiocytosis, a condition that frequently develops in sJIA patients. Our analyses of this dataset have produced intriguing preliminary results and we are actively undertaking follow-up investigations to understand their implications. Beyond the INCHARGE collection, we have continued to expand our investigations of individuals and families with systemic arthritis. In April 2018, we launched an NIH Intramural Research Program research protocol entitled Investigation of the Natural History, Genetics, and Pathophysiology of Systemic Juvenile Idiopathic Arthritis, Adult-Onset Stills Disease and Related Inflammatory Conditions (18-AR-0081). This protocol is designed to facilitate broad recruitment of children, adults and families with systemic arthritis to the NIH Clinical Center for family-based genomic sequencing, coupled with systematic, longitudinal characterization of clinical and immunological phenotypes. To date, we have enrolled nearly 100 subjects in this research protocol. 3.Development of treatment guidelines for the treatment of childhood arthritis Together with the American College of Rheumatology and a panel of JIA experts, we developed evidence-based guidelines for the treatment of juvenile idiopathic arthritis. Briefly, research questions were identified and refined by members of the guideline development teams. Systematic literature review was conducted to compile available evidence pertaining to each research question. The quality of evidence was rated using a standardized methodology and a group consensus process was performed by a panel of content experts to generate the final recommendations and grade their strength. Using this process, we developed two sets of treatment guidelines that were published during this reporting period: recommendations for children with juvenile idiopathic arthritis manifesting as non-systemic polyarthritis, sacroiliitis or enthesitis; and recommendations for the screening, monitoring and treatment of uveitis in children with juvenile idiopathic arthritis. Thirty-nine recommendations were developed for polyarthritis, whereas 19 recommendations were developed for JIA-associated uveitis. The majority of recommendations relied heavily on expert consensus because there was a lack of literature with good quality evidence.